1. Field of the Invention
The present invention relates generally to piezoelectric resonator devices referred to as tuning fork type piezoelectric resonator devices, and more particularly, to a piezoelectric resonator device having a structure in which a tuning fork type vibrating portion is formed by providing a piezoelectric substrate with slits.
2. Description of the Prior Art
FIGS. 1A and 1B show an example of a conventional tuning fork type piezoelectric vibrator. In the tuning fork type piezoelectric vibrator 1, a piezoelectric substrate 2 almost rectangular in shape is provided with a slit 3. On the upper surface of the piezoelectric substrate 2, an electrode 4a is provided in the vicinity of the slit 3 and an electrode 4b is provided spaced apart from the electrode 4a by a predetermined distance around the periphery of the piezoelectric substrate 2. On the other hand, as shown in FIG. 1B, on the lower surface of the piezoelectric substrate 2, a common electrode 5 is formed so as to be opposed to the electrodes 4a and 4b through the piezoelectric substrate 2.
The electrodes 4a and 4b formed on the upper surface of the piezoelectric substrate 2 are respectively used as input and output terminals, or vice versa, thereby causing portions on both sides of the slit 3 provided in the piezoelectric substrate 2 to be vibrated so as to widen or narrow the slit 3.
FIGS. 2A and 2B illustrate a tuning fork type piezoelectric vibrator having a structure for facilitating electrical connection to the exterior added to the above described tuning fork type piezoelectric vibrator 1. In this tuning fork type piezoelectric vibrator 6, a piezoelectric substrate 7 is provided with a slit 8. As shown in FIG. 2A, on the upper surface of the piezoelectric substrate 7, an electrode 9a formed around the slit 8 is electrically connected to a connecting electrode 10a formed in a non-vibrating region. In addition, a pair of electrodes 9b are formed spaced apart from the electrode 9a by a predetermined distance and are electrically connected to connecting electrodes 10b formed in the non-vibrating region, respectively. Lead terminals 11a, 11b, to 11c are respectively joined to the connecting electrodes 10a and 10b. On the other major surface of the piezoelectric substrate 7, a common electrode 12 is formed.
In use, the lead terminals 11a and 11c are electrically connected to each other outside of the tuning fork type piezoelectric vibrator 6.
In the tuning fork type piezoelectric vibrator 6 as shown in FIGS. 2A and 2B, the oscillation frequency thereof is adjusted depending on dimension such as the length of the slit 8 and the width of a piezoelectric substrate portion where the electrodes 9a and 9b are formed. Utilizing the vibration of a tuning fork has the advantage that a small-sized resonator having a wide frequency range of tens to several hundreds of kilohertz can be constructed by adjusting the above described length of the slit and the basic width of the substrate. In order to make the most of this advantage, the connecting electrode portions must be arranged in as small an area as possible.
However, when the lead terminals 11a to 11c are joined by soldering, there is a limit to how much the size of the soldering portions can be reduced. Accordingly, the sizes of the connecting electrodes 10a and 10b can not be so reduced.
Consequently, it has also been considered to change the plane shape of the piezoelectric substrate 7 so as to enlarge the portion where the connecting electrodes 10a and 10b are formed, while making small only the vibrating portions on both sides of the slit 8. If the plane shape of the piezoelectric substrate 7 is thus changed, however, it becomes difficult to cut the piezoelectric substrate 7 from a mother substrate. In addition, a useless portion occurs in cutting down the piezoelectric substrate 7 from the mother substrate. Accordingly, the modified tuning fork type piezoelectric vibrator 6 has the disadvantage of being increased in cost.